WITH depart AS (SELECT source AS s FROM ways WHERE gid=10213),
arrivee AS (SELECT target as t FROM ways where gid=64552)
INSERT INTO test(the_geom) SELECT ST_UNION(the_geom)
FROM dijkstra_sp('ways', depart.s, arrivee.t);

but any of my experiments worked; any idea someone, please??

Edit: Thanks to dkastl, I wrote the following, certainly not optimized but still working one-line function to get a path from coordinates :